1. Field of the Invention
The present invention relates to a method and apparatus for ablating human fat by ultrasonically destroying cells.
2. Description of the Background Art
Adipose tissue, more commonly known as “fat,” is formed of cells containing stored lipid. Fat cells are very large, ranging up to 120 microns in diameter. They are typically spherical, but may assume polyhedral shapes because of mutual deformation. A single droplet of lipid occupies most of the volume of the cell. The nucleus of the cell is displaced to one side by the accumulated lipid and the cytoplasm is reduced to a thin rim comprising only about one fortieth of the total volume of the cell. Each cell is surrounded by delicate reticular fibers. Capillaries are found in the angular spaces between the cells. Capillaries form a loose plexus throughout the adipose tissue. Adipose tissue appears in section as a delicate network with large polygonal meshes.
Adipose tissue is often subdivided into small lobules by connective tissue septa. This compartmentalization, visible with the naked eye, is most obvious in regions where the fat is subjected to pressure. In other regions, the connective tissue septa are thinner and the lobular organization of the tissue is less apparent.
Adipose tissue is widely distributed in the subcutaneous tissue, but exhibits regional differences in amount. Those regional differences are influenced by age and sex. In infants and young children there is a continuous subcutaneous layer of fat, the panniculus adiposus has a rather uniform thickness over the whole body. In adults the panniculus adiposus thins out in some regions but persists and grows thicker in certain sites of predilection. These sites differ in the two sexes and are largely responsible for the characteristic differences in body form of males and females. In the male, the principal areas are the neck and the region overlying the seventh cervical vertebra, the subcutaneous area overlying the deltoid and triceps, the lumbrosacral region, and the buttocks. In the female, subcutaneous fat is most abundant in the anterior neck, the breasts, the buttocks, the epitrochanteric region, and the anterior aspect of the thigh. Few blood vessels pass through subcutaneous fat into the overlying skin, which receives its nutrients through a subdermal plexus of blood vessels that run above the fatty layer.
In addition to the aforementioned fat deposits, there are extensive accumulations in both the sexes in the omentum, mesenteries, and retroperitoneal areas. All of the aforementioned areas readily give up their stored lipid during fasting. There are other areas of fat, however, that do not give up their stored fuel so readily. For example, the adipose tissue in the orbit, in the major joints, and on the palms of the hands and soles of the feet does not seem to be grist for the metabolic mill, but instead has the mechanical function of support or protection. These areas diminish in size only after very prolonged starvation.
An excess of adipose tissue, i.e., obesity, may be unhealthful because it gives rise to varying health problems in human beings, both physical and psychological in nature. Beyond psychological effects such as poor self-image, obesity typically increases the risk of conditions such as heart disease, high blood pressure, osteoarthritis, bronchitis, hypertension, diabetes, deep-vein thrombosis, pulmonary emboli, varicose veins, gallstones and hernias.
Thus, there is a clear need for methods capable of removing fatty tissue. Dieting or learning good eating habits are effective to a degree but are not long-range solutions for most people; nor are these approaches effective in situations where undesirable fatty deposits are localized in the body.
Liposuction extracts adipose tissue from the body by purely mechanical means. If fat cells are destroyed after puberty, the remaining fat cells will attempt to compensate to some degree, but about 70% of the fat contained in the destroyed cells is never recovered by the body. The permanent removal of fat from the human body is a highly desirable but very difficult undertaking. Liposuction, however, is a highly invasive and potentially disfiguring procedure associated with a prolonged and uncomfortable recovery due to the resulting separation of the skin from the body. For that reason, liposuction is not practical for weight control therapy, but may be practical body reshaping only in limited areas.
Electromedical methods and apparatus have been used in the past for various surgical and therapeutic procedures. For example, U.S. Pat. No. 4,527,550 to Ruggera et al., discloses a radio frequency diathermy apparatus including means for localizing the heat focus. U.S. Pat. No. 4,397,313 to Vaguine discloses a microwave hyperthermia apparatus including means for producing a concave electric field for focusing the electromagnetic energy at a particular region of the body. Federal Republic of Germany Patent 2,508,494 to Schultz, U.S. Pat. No. 4,343,301 to Indech, and U.S. Pat. No. 3,958,559 to Glenn et al., relate to ultrasound devices that can be focused on a tumor, for example, within the body.
However, these aforementioned systems have not been used for removal of fatty tissue. In fact, some systems recognize the need to avoid damage to adipose or other tissue surrounding the tissue to be destroyed. See, e.g., U.S. Pat. No. 3,958,559 at col. 1, lines 24-25; U.S. Pat. No. 4,397,313 at col. 2, lines 45-57. See also U.S. Pat. No. 4,601,296 to Yerushalmi, which notes at col. 1, lines 30-46 that known devices are capable of automatically controlling the undesired RF heating of healthy tissue. These devices monitor the temperature adjacent the work site, and responsively control the operation of the antenna and of a cooling system.
U.S. Pat. No. 4,397,314 to Vaguine, points out at col. 1, line 54-col. 2, line 11, that healthy tissues are heated by prior art hyperthermia systems less effectively than tumors, since healthy tissue is characterized by a developed blood vessel network and a normal vasodilation response to heat, whereby blood flow may increase threefold after five minutes of heating, for example. On the other hand, tumors are characterized by a damaged blood vessel network and a blood flow that collapses during heating.
U.S. Pat. No. 4,441,486 to Pounds relates to ultrasound hyperthermia. This patent acknowledges the need to control the coverage of the hyperthermia treatment, but points out that with ultrasound this is not a great problem, since ultrasound does not preferentially heat fatty tissue.
U.S. Pat. No. 5,143,063 to Fellner is understood to relate to treatments of adipose tissue using ultrasound energy, or alternatively, microwave or radio frequency waves. The patent does not, however, discuss imaging techniques that ensure treatment regions are covered by the treatment energy.
U.S. Pat. No. 6,071,239 to Cribbs is understood to teach a HIFU array used in a method of selectively destroying fat cells. The patent, however, does not reasonably teach tracking and imaging the progression of the treatment zones.
According to Fritzsche, “With FDA Approval and Reimbursement in Place, Hyperthermia is Fourth Major Anti-cancer Weapon,” The Medical Business Journal, March 1986, at 80-82, one capacitive RF hyperthermia device manufactured by Yamamoto in Japan is effective only where there is a low percentage of body fat.
The disclosures of the above-referenced patents and materials are incorporated by reference herein.
Thus, there is a recognition by the art that adipose tissue should not be heated inadvertently during hyperthermia, and a further recognition that adipose tissue, being more effectively blood-cooled than tumor tissue, is inherently unlikely to inadvertently receive a damaging energy dosage during hyperthermia treatment by means of the prior art systems intended for treatments of tumors or the like.